It would be nice if we could have more than one house per account. Perhaps a total amount of square feet per account, so you could have, for instance, an 18x18 and an 8x8 OR two 14x14s. It would bring some variety to player houses, rather than all the 18x18 boxes littering the landscape.
However, it should not be one house per shard, that would be a nightmare for customer support. A and B would make a deal that A will hold a house for B on Baja and B will hold a house for A on Atlantic. Great, they each have access to two houses on their home shard for the negligible price of holding a house on a shard they don't even play. Until something goes wrong. Maybe A turns out to be a scammer who was just waiting for B to fill up that house with rares, maybe they get in a fight, maybe one of them gets hacked. Whatever it is, there will be much whining to EA and here on the boards (and, even more annoying, much piety from posters who don't have a cross-shard house).